This invention relates to a method of preparing 4-trifluormethyl-2-nitrobenzoic acid and a novel isomer, viz., 4-trifluoromethyl-3-nitrobenzoic acid.
4-Trifluoromethyl-2-nitrobenzoic acid (abbreviated to 4-TFM-2-NBA) is a compound useful as an intermediate material of some medicines, agricultural chemicals and liquid crystals, and the novel isomer too will be useful for similar purposes.
It is known to obtain 4-TFM-2-NBA by the steps of first converting 4-trifluoromethyl-2-nitroaniline into 4-trifluoromethyl-2-nitrobenzonitrile by Sandmeyer reaction and then hydrolyzing the nitrile (Chem. Abstr., 49, 3897b (1955) ). The product of this process is fairly high in purity as indicated by the reported melting point of 140.degree.-140.5.degree. C. However, this process is not suitable for industrial practice because of involving problems such as difficulty of industrially preparing the starting material, 4-trifluoromethyl-2-nitroaniline, use of a very toxic cyanide in the essential Sandmeyer reaction and complicatedness of the operations.
Another known method for preparing 4-TFM-2-NBA is nitrating 4-trifluoromethylbenzoic acid (Chem. Abstr., 64, 3487f (1966) ). However, the product of this method must be low in purity since the reported melting point of the reaction product, 109.degree.-111.degree. C., differs considerably from the aforementioned melting point.